Method for reforming base surface, method for manufacturing semiconductor device and equipment for manufacturing the same

ABSTRACT

The present invention relates to a method for reforming a surface of a base layer before thin film deposition, wherein a base thermal SiO 2  film  1   a  is exposed to any gas for reforming the surface of the base layer selected from the group consisting of AX 4 , AH n Cl 4−n  and AR n X 4−n , (in which, a represents any one selected from the group consisting of Si, Ge and Sn, X represents any one selected from the group consisting of I, Br, F and Cl and R represents any one of C m H 2m+1 , and an accompanying character “n” is any one of 1, 2 or 3 and an accompanying character “m” is a natural number).

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method for reforming a base surface before thin film deposition, a method for manufacturing the semiconductor device and an equipment for manufacturing the same, and more particularly to the method for reforming the base surface before the thin film deposition, the method for manufacturing the semiconductor device and the equipment for manufacturing the same in the thin film deposition by CVD (Chemical Vapor deposition) method using O₃/TEOS (Tetraehylorthosilicate) system reaction gas (the gases containing O₃ and TEOS).

[0003] 2. Description of the Prior Art

[0004] Recently, it is often known that a property of the film formed on the base layer is greatly influenced depending upon a surface condition of the base layer.

[0005] Especially, a film property of CVD film deposited by the CVD method using O₃/TEOS system gas for thin film deposition depends upon the surface condition of the base layer greatly. For example, the growth rate of the thin film is reduced remarkably and the deposited film becomes porous in case that the surface of the base layer is hydrophilic.

[0006] Therefore, the fluidity, the flatness, the embedding ability and the step-coverage ability of the film deposited on a surface of a base layer are lowered.

[0007] It is thought that such deposition irregularity is caused by that an intermediate generated in the reaction of O₃ gas and TEOS gas is a polymer with hydrophilicity, and it is shown that a film can not be deposited on the surface of the base layer in case that the surface of the base layer is hydrophilic.

[0008] As methods destroying a dependence on the surface of the base layer described above, there have been

[0009] (1) a method by plasma processing using the gases such as NH₃, H₂ or the like,

[0010] (2) a method using the insulating film formed using a low concentration of O₃ as the base layer,

[0011] (3) a method using the insulating film formed by a plasma CVD method as the base layer,

[0012] (4) a method processing the surface of the base layer before the thin film deposition with alcohol, or the like.

[0013] However, there are the problems as described below in the mentioned-above method. That is,

[0014] (1) In the method by plasma processing using the gases such as NH₃ , H₂ or the like the good film in the embedding ability and the step-coverage ability has been not deposited, when depositing film on very narrow regions such as via-holes and contact holes.

[0015] (2) In the method using the insulating film formed by a plasma CVD method as the base layer, it has been difficult to form the insulating film being used as the base layer on the very narrow regions such as the via-holes and the contact holes.

[0016] (3) In also the method using the insulating film formed by the plasma CVD method as the base layer, it has been difficult to form the insulating film being used as the base layer on the very narrow regions such as the via-holes and the contact holes as the same as the item (2).

[0017] (4) In the method processing the surface of the base layer before the thin film deposition with alcohol, the effect of reform is poor in reproduction, in addition, the effect of reform processing of the base surface can not be maintained.

SUMMARY OF THE INVENTION

[0018] The object of the invention is to provide a method for reforming a base surface before the thin film deposition, a method for manufacturing the semiconductor device and an equipment for manufacturing the same, capable of maintaining the effect by means reform of the base layer surface, of improving the fluidity, the flatness, the embedding ability and the step-coverage ability of the film deposited on the surface of the base layer and, especially, of improving the embedding ability and the step-coverage ability of the film formed in the very narrow regions such as the via-holes and the contact holes of the base layer.

[0019] In the invention, reform of the surface of the base layer in a reaction chamber is performed by the gas for reform of the base layer surface containing a halogen element, and subsequently, film deposition can be performed on the surface of the base layer reformed by the gas for thin film deposition.

[0020] According to experiments of the inventor of this application, it has been found that when reform of the surface of the base layer is performed by the gas for reform of the base layer surface containing a halogen element, the effect of reform of the base layer surface can be maintained for the long term as compared to the prior art, in addition, the fluidity, the flatness, the embedding ability and the step-coverage ability of the film formed on the reformed surface of the base layer can be improved.

[0021] Especially, the embedding ability and the step-coverage ability of the film formed in the via-holes or the like could be improved, even though there are the very narrow-concave regions such as the via-holes and the contact holes in the base layer.

[0022] Moreover, the fluidity, the flatness, the embedding ability and the step-coverage ability of the film formed on the surface of the base layer thereof can be improved, when reform of the surface of the base layer is performed while heating the base layer.

[0023] Especially, it was confirmed that the effect further can be increased when setting a heating temperature at 100° C. or more upon reform of the surface.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1A to FIG. 1C are sectional views showing a method for reforming a base surface of embodiment of the invention.

[0025]FIG. 2 is a view showing a condition of a base thermal SiO₂ film surface soon after forming the base thermal SiO₂ film, according to the method for reforming the base surface of the embodiment of the invention.

[0026]FIG. 3A and FIG. 3B are views showing a condition of the base thermal SiO₂ film surface before reforming according to the method for reforming the base surface of the embodiment according to the invention.

[0027]FIG. 4A to FIG. 4F are views showing a reaction of the base thermal SiO₂ film and a reaction gas SiCl₄ according to the method for reforming the base surface of the embodiment according to the invention.

[0028]FIG. 5 is a schematic construction view showing a CVD thin film deposition equipment of a cold wall system according to the method for reforming the base surface of the embodiment of the invention.

[0029]FIG. 6 is a side view showing a detail of reforming gas supply means provided on the equipment for manufacturing the semiconductor device according to the embodiment of the invention.

[0030]FIG. 7A and FIG. 7B are section views showing a reaction equipment of a hot wall system according to the equipment for manufacturing the semiconductor device of the embodiment of the invention.

[0031]FIG. 8 is a section view in case of that a O₃/TEOS SiO₂ film is formed after reform processing according to the embodiment of the invention.

[0032]FIG. 9 is a section view in case of that a O₃/TEOS SiO₂ film is formed without performing reform processing of the base surface according to the comparison example.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0033] Hereinafter, the embodiment of the invention will be described referring to the accompanying drawings.

[0034]FIG. 5 is a schematic construction view showing a CVD thin film deposition equipment of a cold wall system according to the method for reforming the base surface of the embodiment of the present invention and FIG. 6 is a side view showing detail of reforming gas supplying bombe.

[0035] A holding table 62 for holding a silicon wafer 1 is provided in a reaction chamber 61 ( a chamber) made of stainless steel, and a heater (a heating means) for heating the silicon wafer 1 is embedded in the holding table 62.

[0036] A conduit 68 a introducing the O₃/TEOS gases (gases for thin film deposition) supplied from a gas supply means 63 or the gas for reforming the base layer surface into the reaction chamber 61 and a gas distribution plate 64 discharging the O₃/TEOS gases or the gas for reforming the base layer surface to the silicon wafer 1 on the holding table 62, said the gas distribution plate 64 being connected to the other end of said conduit 68 a, are installed in the reaction chamber 61. Moreover, an exhaust equipment 65 for adjusting a pressure in the reaction chamber 61 is connected to the reaction chamber 61.

[0037] The gas supply means 63 is comprised of a reforming gas supply means 66, a supply means of the gas for thin film deposition 67, a conduit 68 b and a selecting valve 69 (a selection means).

[0038] The reforming gas supply means 66 supplies the reforming gas in the reaction chamber 61 upon reforming the base surface, and the supply means 67 of the gas for thin film deposition supplies a mixed gas of the O₃/TEOS gases of the gas for thin film deposition after reforming the surface of the base layer.

[0039] The conduit 68 b and 68 c are connected to these two gas supply means 66 and 67 respectively, in addition, these conduits 68 b and 68 c are connected with the conduit 68 a extending into the reaction chamber 61. The connecting ports of these three conduits 68 b , 68 c and 68 a are provided with the selecting valve 69 and the valve selects a flow passage so as to allow to conduct the flow passage introducing the gas for reforming from the conduit 68 b to the conduit 68 a or to conduct the flow passage introducing the gas for thin film deposition from the conduit 68 c to the conduit 68 a.

[0040] The gas for reforming or the gas for thin film deposition are introduced into the reaction chamber 61 through the conduit 68 a selectively by selection of the flow passage by the selecting valve 69.

[0041] The detailed structure of the reforming gas supply means 66 is as follows:

[0042] namely, the reforming gas supply means 66 comprises an evaporation container 72 in which liquid sources such as liquid SiCl₄, SiBr₄, SiF₄ are accommodated and a temperature regulator 71 for adjusting a temperature of the liquid sources in the evaporation container 72, said the temperature regulator being provided around the evaporation container 72 as shown in FIG. 6. Moreover, the reforming gas supply means 66 comprises the conduit 68 d for introducing N₂, H₂ or Ar gas as carrier gas into the liquid sources in the reaction container 72 and the conduit 68 b introducing a source gas (a reforming gas) generated by allowing to bubble the carrier gas in the liquid sources outside the evaporation container 72. A flow meter 73 for measuring flow rate of N₂, H₂ or Ar gas and a valve 74 for performing flow regulation are provided on the conduit 68 d and a valve 75 for performing flow regulation of the reforming gas is provided on the conduit 68 b. The reforming gas generated in the evaporation container 72 is introduced into the reaction chamber 61 through the conduit 68 b.

[0043] Subsequently, the method for reforming the base surface of the embodiment of the present invention will be described.

[0044]FIG. 1A to FIG. 1C are sectional views showing a method for reforming a base surface of embodiment of the present invention.

[0045]FIG. 2 is a view showing a condition of a base thermal SiO₂ film surface soon after forming the thermal SiO₂ film as the base layer (hereinafter referred to as a base thermal SiO₂ film also) is formed, FIG. 3A and FIG. 3B are views showing a conditions of the base thermal SiO₂ film surface before reforming and FIG. 4A to FIG. 4E are views showing a reaction of the base thermal SiO₂ film and the reforming gas SiCl₄ at the base thermal SiO₂ film surface.

[0046] First, the silicon wafer 1 is fed in an oxidation furnace to be heated at 1100° C. within an oxygen atmosphere. By this treatment, the surface of the silicon wafer 1 is oxidized, whereby the thermal SiO₂ film 1 a is formed as shown in FIG. 1A. This thermal SiO₂ film 1 a becomes the base layer for thin film deposition. There are dangling bonds in Si of the surface of a base thermal SiO₂ film 1 a soon after being formed as shown in FIG. 2.

[0047] In this process, a plasma enhanced CVD method and a low pressure CVD method or the like may be used. At this point of time, it is considered that there are occurred the conditions that the surface of the base thermal SiO₂ film 1 a contacts with air (containing moisture) to hydrate to allow to bond Si and OH to form Si—OH bond as shown in FIG. 3A, or to allow to bond Si and H₂O to form Si—H₂O bond as shown in FIG. 3B. In any events, the base thermal SiO₂ film 1 a becomes hydrophilic.

[0048] Subsequently, the silicon wafer 1 is placed on the holding table 62 in the reaction chamber 61 as shown in FIG. 1B to be heated 100° C. or more by the heater built in the holding table 62. And then, the gas for reforming the base layer surface containing SiCl₄ is supplied from the reforming gas supply means 66 to the reaction chamber 61. The gas for reforming the base layer surface is discharged to the surface of the base thermal SiO₂ film 1 a formed on the silicon wafer 1.

[0049] At this time, it can be estimated that two kind of reactions are occurred between the base thermal SiO₂ film 1 a and the gas for reforming the base layer surface on the surface of the base thermal SiO₂ film 1 a as described below. A mark “X” in FIG. 1B shows the situation that this reaction is occurred.

[0050] The situation of the reaction is described, dividing into the base thermal SiO₂ film 1 a terminated by the Si—OH bond and the surface of the base thermal SiO₂ film 1 a terminated by the Si—H₂O bond.

[0051] First, the situation of the reaction of the case being terminated by the Si—OH bond is illustrated.

[0052] As shown in FIG. 4A, —H in —OH being bonded by Si—OH bond and —Cl in SiCl₄ are bonded on the surface of the heated base thermal SiO₂ film 1 a by being exposed to SiCl₄ to generate HCl. By this reaction, O remains in the bond of Si of the surface of the base thermal SiO₂ film 1 a, as well as —Cl is removed from SiCl₄ to generate SiCl₃. Moreover, HCl generated is discharged out of the reaction region of the surface of the base thermal SiO₂ film 1 a, since the temperature of the surface of the base thermal SiO₂ film 1 a is 100° C. or more.

SiCl₄+OH⁻→SiCl₃+HCl+O²⁻.

[0053] Oxygen and Si of the surface of the base thermal SiO₂ film 1 a are bonded to result in SiO.

[0054] Subsequently, SiCl₃ generated and Si—O of the surface of the base thermal SiO₂ film 1 a react as shown in FIG. 4B, whereby Cl and O are replaced to generate SiOCl₂ and Si—Cl as shown in FIG. 4C.

SiCl₃+O²⁻→SiOCl₂+Cl⁻.

[0055] By this reaction, hydrophobicity is appeared, since the surface of the base thermal SiO₂ film 1 a is halogenated.

[0056] Furthermore, even though Cl and O are remained as it is without being replaced, hydrophobicity is shown since the surface is oxidized as shown in FIG. 4D.

[0057] Under the condition that Si of the surface of the base thermal SiO₂ film 1 a is bonded with H₂O, SiCl₄ and H₂O react as shown in FIG. 4E to generate SiOCl₂, HCl and Cl through the same reaction processes as described in FIG. 4A to FIG. 4D.

SiCl₄+H₂O→SiOCl₂+2HCl+Cl⁻

[0058] As a result, it is considered that since Si of the surface of the base thermal SiO₂ film 1 a and Cl are bonded and the surface of the base thermal SiO₂ film 1 a is chlorinated as shown in FIG. 4F, whereby hydrophobicity is appeared.

[0059] After the reform processing described above, without providing processing such as cleaning on the surface of the base thermal SiO₂ film 1 a, the transfer to a subsequent thin film deposition process can be performed. Therefore, the reforming gas is stopped in succession the reform processing described above, and the mixed gas of the O₃/TEOS gases is supplied into the reaction chamber 61 as the gas for thin film deposition from the supply means 67 of the gas for thin film deposition.

[0060] Moreover, the silicon wafer 1 is heated at approximate 400° C. to allow to react the O₃ and TEOS gases thermally.

[0061] Holding the condition for the given time period, an O₃/TEOS SiO₂ film 2 is formed on the base thermal SiO₂ film 1 a as shown in FIG. 1. This O₃/TEOS SiO₂ film 2 shows the SiO₂ film formed by making to react the O₃ gas and the TEOS gas.

[0062] In this embodiment, the thin film deposition is performed using the gases after reforming the surface of the base thermal SiO₂ film 1 a into hydrophobic, whereby the fluidity, the flatness, the embedding ability and the step-coverage ability of O₃/TEOS SiO₂ film 2 formed can be improved.

[0063] Especially, it has allowed to maintain the effect of the reform since using the reforming gas containing a halogen element. That is, even though after performing reform of the base surface, the surface of the base thermal SiO₂ film 1 a is exposed to air for 24 hours subsequently to form the O₃/TEOS SiO₂ film 2, the fluidity, the flatness, the embedding ability and the step-coverage ability of the O₃/TEOS SiO₂ film 2 formed can be maintained.

[0064] Hydrophobicity can be improved, since the temperature of the surface of the base thermal SiO₂ film 1 a is 100° C. or more. In this case, it is considered that silanol (here, Si(OH)₄ is applicable) is generated in reforming process, and silanol is decomposed by the temperature of 100° C. or more. Moreover, when silanol is generated it takes long time to decompose silanol if being less than 100° C., so that the time period to stay on the surface of the base thermal SiO₂ film 1 a becomes long, whereby conversion from hydrophilicity to hydrophobicity becomes difficult.

[0065] Hereinafter, the example actually embodied will be described referring to the FIG. 8. In this example, the invention is applied to the base layer in which there are grooves narrow in width. Moreover, for comparison, a comparison example deposited on the base layer without performing reform processing of the invention is shown in FIG. 9.

[0066]FIG. 8 is a section view in case of that a O₃/TEOS SiO₂ film is formed after performing reform processing on the base surface, and FIG. 9 is a section view in case of that a O₃/TEOS SiO₂ film is formed without performing reform processing of the base surface.

[0067] As shown in FIG. 8, a groove 3 of approximate 0.1 μm in width and approximate 0.6 μm in depth was formed on the silicon wafer 1 to form the base thermal SiO₂ film 1 a on the surface of the silicon wafer 1 having this groove 3 to provide as the base layer. And then, the O₃/TEOS SiO₂ film 2 is formed on the base layer surface thereof, and it was searched whether the embedding ability and the step-coverage ability of the O₃/TEOS SiO₂ film 2 formed could be improved or not.

[0068] Heating temperature is set at 1100° C. in order to form the base thermal SiO₂ film 1 a.

[0069] As the conditions for reform of the base surface, liquid SiCl₄ in 20° C. was used as a liquid source, and bubbling was performed for about 2 minutes by introducing N₂ gas into this SiCl₄ at the rate of 5 littler per min.. Moreover, heating temperature of the silicon wafer 1 was set at 250° C.

[0070] Moreover, in the conditions for thin film deposition of the O₃/TEOS SiO₂ film 2, the ozone concentration in the gas for thin film deposition composed of the mixed gas of the O₃/TEOS was set at a so called high concentration of O₃ concentration of 5 percent in O₂, and heating temperature of the silicon wafer 1 was set at 400° C.

[0071] It is found from FIG. 8 that the O₃/TEOS SiO₂ film 2 of which surface is planarized is formed without voids, when the O₃/TEOS SiO₂ film 2 is formed after performing the processing using the method for reforming the base surface of this embodiment.

[0072] In contrast with this, it is found that the voids are occurred, the surface of the film 2 becomes wavy, whereby a planarized film can not be obtained as shown in FIG. 9, when the O₃/TEOS SiO₂ film 2 is formed without reform processing of the base surface.

[0073] As described above, the embedding ability and the step-coverage ability of the film 2 formed in the groove 3 can be improved, when the surface reform of the base layer 1 a having the very narrow-concave regions such as the groove 3 is performed by the gas for reform of the base layer surface containing a halogen element.

[0074] In this embodiment, although the same chamber 61 is used without separating the reaction chamber used for reforming the base surface and the reaction chamber used for depositing the O₃/TEOS SiO₂ film 2, an individual reaction chamber may be used respectively.

[0075] Moreover, the reaction chamber 61 may be a single wafer processing reaction chamber or a batch processing equipment of a furnace type.

[0076] Furthermore, although the reaction equipment of a cold wall system is used in this embodiment, the reaction equipment may be a reaction equipment of a hot wall system as shown in FIG. 7 and a horizontal type furnace as shown in FIG. 7A or a vertical type furnace as shown in FIG. 7B.

[0077] In this case, a heater or an infrared heating equipment provided on the vicinity of the reaction chamber can be used as the heating means of the hot wall system.

[0078] Besides, although SiCl₄ in the gas expressed by a generalized formu1 a AX₄ is used as the reforming gas, the other gas, for example, SiI₄, SiBr₄ or SiF₄ expressed by a generalized formu1 a AX₄ can be used. Furthermore, the gas, for example, SiHCl₃, SiH₂Cl₂ or SiH₃Cl expressed by a generalized formu1 a AH_(n)Cl_(4−n) (the accompanying character “n” is any one of 1, 2 or 3) can be used. Moreover, the gas, for example, Si(C_(m)H_(2m+1))Cl₃, Si(C_(m)H_(2m+1))₂Cl₂, Si(C_(m)H_(2m+1))₃Cl expressed by a generalized formu1 a AR_(n)X_(4−n) (the accompanying character “m” is a natural number) can be used.

[0079] Moreover, in the generalized formu1 a described above, A represents any one of Si, Ge or Sn, X represents any one of I, Br, F or Cl and R represents any one of C_(m)H_(2m+1). Furthermore, although SiO₂ film is used as the insulating film formed on the base layer, any one of PSG (Phosphosilicate glass) film, BSG (Borosilicate glass) film or BPSG (Borophosphosilicate glass) film can be used. The mixed gas of O₃ and TEOS and TMP (Trimehtylphosphite: P(OCH₃)₃) or TMOP (Trimehtylphosphite: PO(OCH₃)₃) as the gas for thin film deposition where PSG film is deposited, the mixed gas of O₃ and TEOS and TMB (Trimehtylborate: B(OCH₃)₃) as the gas for thin film deposition where BSG film is deposited, and the mixed gas of O₃ and TEOS and TMB and TMP or TMOP as the gas for thin film deposition where BPSG film is deposited can be used.

[0080] As described above, according to the present invention, after the surface of the base layer is exposed to the gas for reform of the base layer surface containing a halogen element to reform the surface of the base layer, the thin film deposition is performed on the surface of the base layer reformed by the gas for thin film deposition.

[0081] The effect of reform of the base layer surface can be maintained, since the gas for reform of the base layer surface containing a halogen element is used. The micronization and the increase in density of the device can be also realized, since the excellent film in the embedding ability and the step-coverage ability can be deposited on the surface of the base layer 1 a having the very narrow-concave regions in width such as the groove. 

What is claimed is:
 1. An equipment for manufacturing semiconductor device comprising: a reaction chamber for reforming a surface of a base layer further to deposit a film on the surface of the base layer after the reform; a holding table for holding said base layer, said holding table being provided in said reaction chamber; a reforming gas supply means for supplying any gas for reforming the surface of the base layer in any one selected from the group consisting of AX₄, AH_(n)Cl_(4−n) and AR_(n)X_(4−n) (in which, a represents any one selected from the group consisting of Si, Ge and Sn, X represents any one selected from the group consisting of I, Br, F and Cl and R represents any one of C_(m)H_(2m+1), and an accompanying character “n” is any one of 1, 2 or 3 and an accompanying character “m” is a natural number) into said reaction chamber; a supply means of the gas for thin film deposition for supplying said gases for thin film deposition into said reaction chamber; and a selection means for selecting a supply of the gas of any one of said gases for reforming the base layer surface and said gases for thin film deposition into said reaction chamber.
 2. An equipment for manufacturing semiconductor device according to claim 1 , further comprising a heating means for heating said base layer.
 3. An equipment for manufacturing semiconductor device according to claim 2 , wherein said heating means is a heater built in said holding table or a heater or an infrared heating equipment disposed on the vicinity of said reaction chamber.
 4. A method for reforming a base surface, wherein a surface of a base layer is exposed to any gas for reforming the surface of the base layer in any one selected from the group consisting of AX₄, AH_(n)Cl_(4−n) and AR_(n)X_(4−n) (in which, a represents any one selected from the group consisting of Si, Ge and Sn, X represents any one selected from the group consisting of I, Br, F and Cl, and R represents any one of C_(m)H_(2m+1), and an accompanying character “n” is any one of 1, 2 or 3 and an accompanying character “m” is a natural number).
 5. A method for reforming a base surface according to claim 4 , comprising concave regions in said base layer.
 6. A method for reforming a base surface according to claim 4 , wherein said base layer is heated, while said surface of the base layer is exposed to said gas for reforming.
 7. A method for reforming a base surface according to claim 6 , wherein temperature of said base layer at heating said base layer is 100° C. or more.
 8. A method for reforming a base surface according to claim 4 , wherein said AX₄ is any one selected from the group consisting of SiCl₄, SiI₄, SiBr₄ and SiF₄.
 9. A method for reforming a base surface according to claim 4 , wherein said AH_(n)Cl_(4−n) is any one selected from the group consisting of SiHCl₃, SiH₂Cl₂ and SiH₃Cl.
 10. A method for reforming a base surface according to claim 4 , wherein said AR_(n)X_(4−n) is any one selected from the group consisting of Si(C_(m)H_(2m+1))Cl₃, Si(C_(m)H_(2m+1))₂Cl₂, and Si(C_(m)H_(2m+1))₃Cl (in which, an accompanying character “m” is a natural number).
 11. An equipment for manufacturing semiconductor device, wherein an insulating film is formed on a surface of a base layer by a chemical vapor deposition method, after reforming the surface of said-base layer by the method for reforming said base surface according to claim 4 .
 12. An equipment for manufacturing semiconductor device according to claim 11 , wherein said insulating film is any one selected from the group consisting of SiO₂ film, PSG film, BSG film and BPSG film.
 13. An equipment for manufacturing semiconductor device according to claim 12 wherein a gas for thin film deposition for forming said insulating film is a mixed gas containing at least a TEOS gas and an O₃ gas. 